JPH0963992A - Formation method of metal layer and formation method of interconnection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metallic layer forming method by which an extremely thin film can be formed by optimizing the vapor-depositing condition of a metal and a metallic wiring forming method for burying a contact hole having a high aspect ratio by using the metallic layer forming method. SOLUTION: The wettability of a substrate which indicates the adsorptivity of sputtered metallic atoms to the substrate is improved by executing the vapor- depositing process of the metallic layer after a wafer is cooled so that the temperature of the wafer can falls within a range from -25 deg.C to room temperature so that the grain boundary energy per unit volume can be increased by the increase of the number of nucleuses generating positions. Therefore, a uniform extremely thin metallic film can be obtained by improving the surface condition of the vapor-deposited metallic layer. In addition, the filling characteristic of a contact hole having a high aspect ratio with aluminum can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly, to a method of forming a metal layer of an ultrathin film and a contact hole having a high aspect ratio to form a metal wiring. The present invention relates to a wiring forming method.

[0002]

2. Description of the Related Art In conventional low-density semiconductor devices, the step coverage when metal is attached is not considered important. However, recently, due to high integration of semiconductor devices, the diameter of contact holes has become extremely small, about half a micron. Further, the impurity implantation region formed in the semiconductor substrate is becoming extremely shallow.

Techniques for burying a metal in a contact hole of a semiconductor device to form wiring include aluminum reflow (Al reflow), high temperature sputtering, and a technique using a high energy laser. Among these, the Al reflow process is advantageous from the viewpoints of mass productivity and process simplification.

However, there are problems in that a high aspect ratio is achieved, and voids are generated due to defective step coverage of aluminum by the sputtering method. In order to solve this, various methods of melting aluminum and filling contact holes have been proposed.

For example, in JP-A-62-132848, JP-A-63-99549 and JP-A-62-109341, after aluminum or aluminum alloy is vapor-deposited, the aluminum or aluminum alloy is heated to a melting point of aluminum or higher. A method of heating aluminum at a temperature of 1 to liquidate aluminum to fill the contact hole is disclosed.

In this method, it is necessary to level the semiconductor wafer in order to properly fill the contact hole with molten liquid aluminum. Further, liquid aluminum shrinks or distorts during solidification so that the surface tension becomes small, and the semiconductor material at the bottom is exposed. In addition, mass productivity is poor because the heat treatment temperature cannot be adjusted accurately. Further, the surface of the metal other than the contact hole becomes rough, and the subsequent photolithography process becomes difficult.

Further, US Pat. No. 4,970,176 discloses a method for forming metal wiring with improved step coverage. That is, after depositing a metal layer having a predetermined thickness at a low temperature (about 200 ° C. or less), 400 to 500 ° C.
Raise the temperature to. Such a metal layer improves the step coverage of a metal layer deposited in a subsequent process through grain growth, recrystallization and bulk diffusion.

Ono, et al., On the other hand, is based on the fact that the liquefaction of Al-Si becomes remarkable when the temperature of the Al-Si film is 500 ° C. or higher.
There has been a proposal of a method of depositing a Si film to fill a contact hole (Hisako Ono, et al., In Proc., 19
90 VMIC Conference June 11-12, pp. 76-82).

Also, Yoda et al. Proposed a method of filling a contact hole by vapor-depositing a metal at a temperature of 500 to 550 ° C. (European Patent Application Publication No. 0387835).
No. 1-61557). According to the method of Yoda et al., The contact hole is completely filled with metal, while the Al-Si film may have strong resistance to electron transfer and weak resistance to stress. Is high. Further, there is a problem that Si contained in the Al film is precipitated at the boundaries between Al particles. Therefore, it is necessary to form the wiring by vapor-depositing the Al-Si-Cu film after etching all the Al-Si films except the contact holes.

Further, CS Park and others including the present inventor are
After depositing an aluminum alloy at a low temperature of 100 ° C. or lower, a method of completely filling contact holes by heat treatment at 550 ° C., which is a temperature below the melting point, for about 3 minutes was proposed (Proc., 1991 VMIC Conference June 11 and 12). pp. 3
26-328). Aluminum deposited at low temperature is 550
Although not melted by heat treatment at ℃, it flows into the contact hole and completely fills the contact hole.

According to the above method of CS Park, etc., 10
A contact hole having a size of 0.8 μm and an aspect ratio of about 1.0 can be completely filled by heat-treating aluminum having a thickness of about 500 Å at a low temperature of 0 ° C. or less. This method does not require the etching step required in the method of Yoda et al. Due to these advantages, the method of filling a contact hole of CS Park and the like has attracted much interest in the field.

Further, in the early stage of semiconductor manufacturing, the metal wiring layer was formed by using pure aluminum, but the aluminum layer absorbs silicon atoms from the silicon substrate by the heating in the sintering process and causes junction spiking. generate. Therefore, Al-1% Si obtained by supersaturating aluminum with silicon has been frequently used as a material for the metal wiring layer.

However, in the case of forming a wiring of a semiconductor device using Al-1% Si, when heat treatment is performed at a temperature of about 450.degree.
Since the residue is formed, the contact resistance of the wiring increases.

A diffusion barrier film is formed between the wiring layer and the silicon substrate or the insulating layer in order to prevent the formation of Al spiking or Si residue due to the above reaction between the metal wiring layer and the silicon substrate. The technology is known.

For example, US Pat. No. 4,897,709 describes a method of forming a titanium nitride film as a diffusion preventing film on the inner wall of a contact hole. Further, in Japanese Patent Laid-Open No. 61-183942, a double film composed of a refractory metal film and a titanium titanium film is formed as a barrier layer and then heat-treated to stabilize the bottom of a contact hole connected to a semiconductor substrate. A method for improving the barrier effect by forming a refractory metal silicide layer made of a thermal compound is disclosed.

In addition, Nishita et al., When forming the diffusion barrier layer, perform heat treatment after forming the TiN layer, and then again perform T
A method for forming an iN layer to improve the barrier effect has been proposed (JP-A-63-97762).

In order to improve the characteristics of the diffusion prevention film in the contact hole in which the diffusion prevention film is formed, it is desirable that an oxide is present at the boundary between the surface of the diffusion prevention film and the particles. However, the presence of this oxide lowers the wettability between the diffusion barrier film and aluminum to form a void, or forms a metal layer having a bad profile during heat treatment. Cause deterioration.

Dipankar et al. Reported Al-1% Cu at 170 ° C.
We have published the experimental results of vapor-depositing alloys on various underlying films (reference: “EFFECT OF UNDERLAYER ON SPUTTERED AL
UMINIUM GRAIN STRUCTURE AND ITS CORRELATION WITH S
TEP COVERAGE IN SUBMICRON VIAS "by Dipankar Parman
ik and Vivek Jain, June 12-13, 1990 VMIC Conferenc
e, pp 332-334). Dipankar et al. Showed that the size of aluminum particles produced during vapor deposition differed depending on the type of underlying film, and that the step coverage of aluminum was closely related to the size of aluminum particles formed during vapor deposition.

From the above technical background, the aluminum reflow process for filling a contact hole having a high aspect ratio is the same as in the aluminum deposition process.
It is understood that it depends on the wettability of the metal layer and the underlying barrier metal and the process parameters relating to these reactions.

For example, if the wettability between Al and its underlying film is not good, voids will be generated from the part with poor wettability in the subsequent heat treatment step. Further, when an underlayer film that reacts with Al is used, the reaction layer generated at the interface is Al
Therefore, it is difficult to fill the contact hole with a homogeneous metal because the mobility of the contact hole is excessively suppressed.

[0021]

SUMMARY OF THE INVENTION An object of the present invention is to provide a metal layer forming method for improving the vapor deposition conditions of a metal layer to form a uniform thin metal layer with high reliability.

Another object of the present invention is to provide a wiring forming method for stably filling a contact hole having a high aspect ratio by using a homogeneous thin metal layer.

[0023]

In order to achieve the above object, a method for forming a continuous metal thin film according to the present invention is a method for forming a metal layer by a physical vapor deposition method,
After the temperature of the wafer is lowered by a cooling process that forcibly cools the wafer for the dense nucleation of atoms that are incident with appropriate energy and are physically adsorbed at a predetermined position on the wafer, It is characterized in that a metal is vapor-deposited.

Preferably, the cooling temperature is -25 ° C. to room temperature.

The metal layer is preferably made of any one of Al, Cu, Ag, Au and W so that it can be used as a wiring material.

According to a preferred embodiment of the present invention, in the forced cooling step, the temperature of the wafer is controlled by using a separate cooling means provided on the back surface of the wafer for circulating a coolant.
A contact cooling method for reducing the temperature to an arbitrary temperature in the range of 25 ° C. to room temperature is used, and any one of liquid nitrogen, He and cooling water can be used as the refrigerant.

According to another embodiment of the present invention, the forced cooling step uses a non-contact type backside gas conduction system, and the cooling conduction gas is an inert gas or H 2 which prevents oxidation of metal. It is also possible to use a reducing gas such as

In order to achieve the above other object, the wiring forming method of the present invention comprises a step of forming an interlayer insulating film on a semiconductor substrate, and a step of forming a contact hole from the interlayer insulating film to the surface of the semiconductor substrate. A step of forming, and a step of depositing a diffusion barrier film on the bottom surface of the contact hole,
Depositing a uniform aluminum or aluminum alloy thin film on the diffusion barrier under vapor deposition conditions having a deposition temperature of -25 ° C. to room temperature, and heat treating the aluminum or aluminum alloy thin film at a temperature below a melting point, And a step of filling the contact hole.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

Usually, in the case of physical vapor deposition (PVD), the metal atom to be vapor-deposited is incident with a corresponding energy, so that the atom physically adsorbed (hereinafter referred to as “adsorbed atom”).
After a certain amount of movement from the incident position, atoms are rearranged on the surface to be deposited. At this time, the atoms lose energy and form stable nuclei, which are condensed toward the surface of the substrate. During the condensation, the degree of nucleation varies depending on the reaction between the adsorbed atoms and the surface of the substrate or the underlying film and the mobility determined by the kinetic energy of the adsorbed atoms.

Therefore, in order to apply the Al reflow process to the sub-half-micron contact having a high aspect ratio, the change in the state of metal atoms was observed while changing the metal vapor deposition conditions. In particular, the wettability (that is, the degree to which the sputtered metal atoms (adsorbed atoms) are easily adsorbed to the underlying film), which is an important factor that determines the reliability of the wiring due to the initial vapor deposition characteristics of the metal thin film, nucleation, grain size, etc. Was examined by the following experiment.

FIGS. 1 to 3 are cross-sectional photographs obtained by observing the state of Al nucleation on the TiN underlayer film with a scanning electron microscope (SEM) while changing the deposition conditions of the aluminum metal film.

That is, FIG. 1 shows the surface of the aluminum film 30a deposited at a high temperature (about 450 ° C.) by the conventional method.
FIG. 2 shows a low temperature (about 2%) without the cooling process according to the present embodiment.
The surface of the aluminum film 30b deposited at 0 ° C. is shown in FIG.
Is vapor deposited by applying the cooling process according to the present embodiment.
1 shows the surface of the thin film 30c.

A silicon substrate is used as the substrate 10, and TiN having a thickness of about 600 Å is used as the base film 20 formed on the substrate 10 at a temperature of 200 ° C., a pressure of 2 mTorr, and Ar:
Deposition was performed under the same deposition conditions such as N2 = 40: 85. A
The 1-films 30a, 30b, 30c were formed by vapor deposition of ultra-thin films of 60 Å.

After depositing an aluminum thin film by a usual method without passing through the cooling step according to the present embodiment, Al
As a result of investigating the continuity of the film in the initial nucleation, the island-shaped grains appeared as shown by the Al films 30a and 30b in the cross-sectional photographs of FIGS.

That is, although the island-shaped grains appear in the Al film deposited on the wafer as the deposition temperature increases, it is understood that a uniform film can be obtained by depositing Al after cooling the wafer. This is cooled by applying the cooling process according to the present embodiment when the adsorbed atoms of Al that are in a high temperature state are adsorbed to the underlying film 20 by sputtering, and the mobility of the adsorbed Al atoms is optimal. This is because the mobility is lowered and the amount of movement of Al atoms becomes an optimum amount.

As can be seen from FIG. 3, while maintaining the wafer 10 between −25 ° C. and room temperature, Al
Alternatively, according to the observation result when an aluminum alloy 30c such as Al-1% Si-0.5% Cu is vapor-deposited with a thickness of 60Å, an extremely dense and uniform film is obtained, and an ultrathin film up to 20Å is obtained. I could get it.

In order to use the metal layer as a wiring material, in addition to Al or Al alloy, it is possible to use any material having excellent electric conductivity such as Cu, Ag, Au and W.

In the preferred embodiment of the present invention, the following two methods are used as the cooling step.

As a first method for lowering the vapor deposition temperature, a non-contact method in which Ar gas at normal temperature is flowed for a predetermined time in the same chamber for vapor deposition of aluminum to forcibly cool the wafer is preferable. In this case, the backside gas conduction method is suitable for effectively cooling the temperature of the wafer. In addition to Ar, an inert gas such as He or a reducing gas such as H ₂ that prevents metal oxidation is suitable as the conductive gas.

The temperature of the wafer chuck at the time of TiN deposition is about 200 ° C. Further, the wafer is heated by the influence of the plasma atmosphere in the chamber.
Cooled by the gas, the mobility of Al atoms is suppressed,
As a result, a dense and uniform Al film is formed.

However, when the same chamber for metal deposition is used as the chamber for performing the cooling step, the temperature of the wafer chuck increases because the wafer is held in the plasma atmosphere for a long time. is there. Therefore, it is desirable to perform the cooling process using another chamber. In this case, the cooling process and the Al deposition process are not continuously performed in the same chamber, so that the temperature rise of the wafer chuck can be prevented. The homogeneity of the deposited Al film can be further improved.

As a second method, a cooling means for circulating a cooling medium to cool the wafer (for example, a separate cooling section (chiller block) is provided outside the deposition chamber, and the cooling section cools the cooling medium). A contact-type cooling method in which a means for cooling the wafer from its rear surface with a cooled coolant is provided and the temperature of the wafer is cooled to an arbitrary temperature of -25 ° C. to room temperature is suitable.

When the Al vapor deposition step is continuously performed after the wafer is cooled in the same chamber by using the cooling means as described above, rather than the first method described above, that is, the cooling step using Ar gas or the like, More dense Al nuclei can be generated.

As the refrigerant in the contact cooling method,
Liquid nitrogen, He gas or cooling water are preferred.

Next, a method of forming a wiring contact in a contact hole having a high aspect ratio by using the metal layer forming method optimized by the above-described method will be described. 4 and 5 are cross-sectional photographs of the result of depositing metal in the contact holes of the substrate 10 having the interlayer insulating film 40 and the TiN barrier layer 20, and FIG. 4 illustrates a case where the cooling process is not performed. Indicates the case where the cooling process was executed.
Note that, for convenience of description, the same reference numerals are given to portions corresponding to those in FIGS. 1 to 3.

The diameter of the contact hole is 0.37 μm,
The aspect ratio is 3, and the vapor deposition conditions for the TiN film 20 and the vapor deposition conditions for the Al films 300a and 300A are the same as those described above. However, the thickness of evaporated Al is about 600.
Å. In the cooling process, Ar gas at room temperature is used in a chamber different from the chamber in which the Al deposition process is performed.
Circulate for 0 seconds.

As is clear from the photograph of the cross section of FIG.
The grain size of the aluminum 300a deposited on the N barrier layer 20 is large, and a part of the sidewall of the contact hole where aluminum is not deposited is also observed. On the other hand, when the cooling process is performed, it is clear from the cross-sectional photograph of FIG. 5 that fine Al grains 300A are uniformly vapor-deposited and the step coverage is improved. This result is similar to the growth of Al grains on the underlying film without contact holes.

FIGS. 6 and 7 are SEM cross-sectional photographs observing the contact burying characteristics after the aluminum reflow step. FIG. 6 shows the case where the cooling step was not executed, and FIG. 7 shows the case where the cooling step was executed. Show.

The heat treatment in the aluminum reflow step was carried out at a temperature of 580 ° C. for 90 seconds. The wafer temperature at this time was about 450 ° C.

As is apparent from the cross-sectional view of FIG. 6, when the reflow process is performed without the cooling process, voids 50 are generated in the portion having poor wettability, and the contact hole is not properly filled.

However, as is clear from the sectional view of FIG. 7, the mobility of the aluminum atom 300B deposited at the deposition temperature from -25 ° C. to room temperature is suppressed, and therefore,
The phenomenon of “sticking” due to migration is reduced and the filling properties of aluminum are improved.

As described above, in order to bury a contact hole having a high aspect ratio by heat-treating the metal film, it is required to densely and uniformly deposit the metal film on the side wall and the bottom surface of the contact hole. This requirement is met by sufficient cooling of the wafer temperature during metal deposition. That is, the higher the vapor deposition temperature of the metal, the higher the mobility of the adsorbed atoms, and the larger the grain size due to the growth of grains, while the lower the vapor deposition temperature as described above, the lower the mobility of the adsorbed atoms ( By optimization, a dense and uniform metal film is formed.

As described above, according to the present embodiment, when the metal such as aluminum is vapor-deposited, the state of nucleation of the metal is improved by sufficiently cooling the wafer to the proper temperature. A dense and uniform metal film is formed even if an ultra-thin film of a certain degree is deposited.

The present invention is not limited to the above embodiment,
Various modifications are possible within the scope of the technical idea of the present invention.

[0056]

According to the present invention, sputtering is performed by performing a cooling process before the metal layer deposition process and performing the deposition process in a state where the temperature of the wafer is in the range of -25 ° C to room temperature. It is possible to improve the wettability, which indicates the degree to which metal atoms are easily adsorbed to the base film, increase the number of nucleation positions, and increase the grain boundary energy per unit volume.

As a result, the surface condition of the vapor-deposited metal layer is improved and a dense and uniform ultrathin metal film is obtained. Further, the filling property of aluminum or the like in the contact hole having a high aspect ratio can be improved.

[0058]

[Brief description of drawings]

FIG. 1 is a photograph showing deposition characteristics of an aluminum film deposited on a diffusion barrier film by a normal high temperature deposition method.

FIG. 2 is a photograph showing deposition characteristics of an aluminum thin film deposited at low temperature without a cooling step.

FIG. 3 is a photograph observing Al vapor deposition characteristics to which a cooling step according to the present embodiment is applied.

FIG. 4 shows a TiN base film in a contact hole,
SE of the result obtained by depositing Al without cooling the wafer
It is an M section photograph.

FIG. 5: On the TiN base film in the contact hole,
The resulting S obtained by depositing Al after cooling the wafer
It is an EM cross-section photograph.

FIG. 6 is a SEM cross-sectional photograph of Al deposited on the contact hole without cooling the wafer after the reflow process.

FIG. 7 is a SEM cross-sectional photograph of Al deposited on a contact hole after cooling a wafer, observed after a reflow process.

Claims (12)

[Claims] 1. A method of forming a metal layer by a physical vapor deposition method, for producing dense nuclei by atoms which are incident with appropriate energy and are physically adsorbed on a wafer,
While cooling the wafer and lowering the temperature of the wafer,
A method for forming a metal layer, which comprises forming the metal layer by a physical vapor deposition method. 2. The method for forming a metal layer according to claim 1, wherein the temperature of the wafer is set between −25 ° C. and room temperature by cooling the wafer. 3. The method for forming a metal layer according to claim 1, wherein the metal layer contains any one of Al, Cu, Ag, Au and W which is a wiring material. 4. The wafer is cooled by using a contact cooling method capable of simultaneously performing cooling and vapor deposition by a mechanism in which a cooling medium is cooled by an external cooling device and the cooling medium is circulated to cool the wafer from the back surface. The method for forming a metal layer according to claim 1, which is performed. 5. The method for forming a metal layer according to claim 4, wherein the refrigerant is one of liquid nitrogen, He, and cooling water. 6. The method for forming a metal layer according to claim 1, wherein the wafer is cooled by using a non-contact type backside gas conduction method. 7. The method for forming a metal layer according to claim 6, wherein the cooling conduction gas in the backside gas conduction method is an inert gas or a reducing gas. 8. A step of depositing a diffusion barrier film on a surface of a contact hole formed in an interlayer insulating film laminated on a semiconductor substrate, and aluminum or aluminum on the diffusion barrier film at a deposition temperature of −25 ° C. to room temperature. A wiring forming method comprising: a step of depositing a thin film of an aluminum alloy; and a step of filling the contact hole by heat-treating the thin film of aluminum or an aluminum alloy at a temperature below a melting point. 9. In the step of depositing a thin film of aluminum or an aluminum alloy, the semiconductor substrate is cooled by an external cooling device, and the semiconductor substrate is cooled by a contact cooling method in which the coolant is circulated to cool the semiconductor substrate from the back surface. 9. The wiring forming method according to claim 8, wherein the temperature is lowered to a range of −25 ° C. to room temperature. 10. The wiring forming method according to claim 9, wherein the coolant is any one of liquid nitrogen, He, and cooling water. 11. The wiring forming method according to claim 8, wherein, in the step of depositing the thin film of aluminum or aluminum alloy, the semiconductor substrate is cooled by a non-contact type back surface gas conduction method. 12. The wiring forming method according to claim 11, wherein the conductive gas for cooling in the back surface gas conductive system is an inert gas or a reducing gas.